August 1,2017, 2:23:13PM,EDT

"A
northward bulge in the jet stream, an area of high pressure at the
surface, intense sunshine and dry soil conditions are responsible for
the extreme heat," according to AccuWeather Senior Meteorologist Brett
Anderson.

The jet stream is a fast river of air
at the level in the atmosphere in which jets cruise. The jet stream
separates heat to the south from cool air to the north.
High
pressure is a large area of sinking, dry air that spins in a slow
clockwise direction. The sinking air heats up as it descends through the
atmosphere. The stronger the area of high pressure, the greater the
amount of heat is produced.
Temperatures are projected to trend downward slightly on Friday, but the more noticeable change will occur this weekend.
"By this weekend, the jet stream will straighten out, and the area of high pressure will weaken," Anderson said.

Interior locations will still be hot during the midday and afternoon, just not as extreme as much of this week.
"Temperatures
on Saturday and Sunday will throttle back between 5 and 15 degrees
Fahrenheit, when compared to most days this week across much of
Washington, Oregon and Idaho," Anderson said.
Highs in the 110s
will be replaced with highs near 100 across the interior hot spots.
Highs near or above 100 over the rest of the interior will be replaced
with highs in the 90s.
In some coastal locations of Washington and Oregon, highs will trend back to the 70s and lower 80s.
Farther
south, in Northern California and Nevada, it may take until the middle
of next week before temperatures lower significantly.RELATED:AccuWeather Severe Weather Center: Heat, fire danger advisoriesTop foods to keep youth athletes hydrated, energized in summerStay fit, happy and hydrated with these 14 warm weather hacksAre we doing enough to fight climate change?
People should continue to limit strenuous activity during the midday and afternoon hours. Be sure to drink plenty of fluids.
The pattern change will reduce the demand for electricity, and air quality may improve as well.
However,
the risk of wildfire ignition and spread will remain elevated, due to
the low chance of shower and thunderstorm activity and dry landscape.

As of Tuesday, Aug. 1, more than 20 wildfires were burning the the three-state area of Idaho, Oregon and Washington, according to the Wildfire Incident Information System. These active fires have consumed more than 265,000 acres.
Officials urge residents and visitors to observe all restrictions on the use of open flames.
People
using power equipment and cooking outdoors to reduce the buildup of
heat in their homes should use caution. Never park over high brush as
the heat from the exhaust system can start a fire. Be sure to extinguish
campfires prior to leaving the vicinity.
In terms of rainfall,
enough moisture may return to the region to produce very spotty
thunderstorms next week. However, some of the storms may bring little or
no rainfall and may raise the risk of lightning-induced wildfires.
"It is possible that heat may again build for a few days during the second week of August," Anderson said.
The
amount and duration of that mid-month heat will depend on the amount of
sunshine and moisture in the region as well as the behavior of other
weather systems across North America.